Electronic coding means for signaling systems



Dec. 5, 1950 c. VOLZ 2,532,870

ELECTRONIC CODING MEANS FOR SIGNALING SYSTEMS Filed May 18, 1949 O '1- Toflecoding I 3 J Him-nits 'T y gDT I N52 I L F' 1 l l 11), l 18 BIZ LnifinQ I 14 Lontzmlled by trail i6 in advance INVENTOR.

C l Volz BY 2 Z HIS ATTORNEY Patented Dec. 5, 1950 UNITED STATES: Q1?

13'Claims. (c1. l ra-35s) invention relates to electronic coding means for signaling systems and particularly to elec.

tronic' coding means for signaling systernsusing coded alternating current.

There are many forms of" signaling systems that use coded alternating current. For example, railway train control systems generally use receiving apparatus that is selectively responsive to alternating current periodically varied at different code rates. Receiving apparatus, com monly calleda receiver, of this type of a train control system is shown in LettersiPatent' of the United States No. 2,462,454, granted on February 22', 1949; to Leslie R. Allison for Train Carried Cab Signal Apparatus. train control system in which-the receivers respond to noncoded alternating current, such a receiver being shown in Letters Patent of the United States No. 2,269,239, granted January 6, 1942, to Leslie R. Allison, for Railway Trafiic Controlling Apparatus.

These train control systems make use of track circuits which are provided with means for sup plying to the rails at the exit end of the track section alternating current according to traflic conditions in advance of the track section. In.- ductors are mounted on the locomotive or train for inductive relation with the rails and an elec: tromotiveforce having the characteristicsof the rail current is induced in the inductors as the locomotive moves through the track section. The electromotive forces picked upby thetrain carried inductors are applied to the. receiver for the operation thereof. Some railroads may have divisions on which a train control and .cab signal system using coded alternating current is in stalled and other divisions on which a system using noncoded alternating current is installed. Heretofore, a locomotive of such a railroad must be equipped with both forms of receivers if the locomotive is to be operated over the difierent divisions and the cab signals used. A ain. a railroad having a cab signal and train control installation in which noncoded alternating current is used may find it desirable to convert such an installation to a system using coded alternating current. The-conversion of such an installation may require some period of time and during the conversion period the locomotives must be equipped with both the old and the new forms of receivers if cab signal protection is to be obtained during the conversion period.

Furthermore, many railroads using coded a1- ternating current for the control of wayside and/ or cab signals providecoding meansior each There is also a type of tracksection; to codethe alternat n QUI QQWHP plied to. the track rails, the. codin me n 91: Q Q.

transmitter havin movin contac s. w ich criodi lly terr pt h curr nt at: difi r ntn o: determined code rates.

In view of the forego n cir umstances, a main object, of my invention. is the prov si n of 6 .3.

Another feature of my invent on 7. Pl?

sion of codingmeans. or code modul itqrs that can .be mounted with a. receiver responsive to coded energy to; operate the receiver when ity is,

being supplied-with noncoded energy.

Still another feature of my invention is t e provision of an electronic coding means of: th type here involved which is small and compact so that. it can be installed in the standard eguipe ment box provided for housing the usual code responsive receiver.

Other features, objects and advantages of my invention will appear as the specification pro: g-resses.

In order to obtain the foregoing objects, features and advantages of my invention, I provide an electron tube oscillator capable of supplying a sinusoidal voltage having the frequency of the code rate or a selected one of the code rates with which an associated receiver responds to ether with a rectifier or asymmetric unit. This voltage of the oscillator is impressed upon the circuit to which the alternating current energy is supplied through the rectifier. For one half cycle of the oscillator voltage the rectifier or asymmetric unit will not, conduct and there is substantially no effect on the alternating current being supplied to the signaling circuit. During the other half cycle of the oscillator voltage the associated asymmetric unit conducts and the path through the oscillator out ut and the asymmetric unit forms a low impedancepath for the alternating signaling current and it in effect shunts the alternating signaling current. In other words the oscillator is a low impedance source connected in multiple with a high impedance signaling source with the result the signaling circuit cdnnected t receive the signaling current is in eiiect short.- circuited at acode rate corresponding to the frequency of the oscillator.

I shall describe one form of apparatus embodying my invention and shall then point out the novel features thereof in claims.

The ompan ng d win e d a am at view showing one form of electronic coding means embodying my invention when used with a train control system that is provided with receivers responsive to coded alternating current and which coding means is here shown as mounted on a train with the receiver for code operation of the receiver when the locomotive on which the receiver is mounted is operated over a track circuit supplied with noncoded alternating current.

It is to be understood that my invention is not limited in its use to train carried apparatus and this one application illustrates the principle of the apparatus, there being many other places where the apparatus is useful.

Referring to the drawing, the reference characters la and lb designate the track rails of a railroad over which traffic normally moves in the direction indicated by an arrow, and which rails are formed by the usual insulated rail joints with a track section DE. This section DE would be one section of a series of track sections of a signal system. The track section DE is provided with a track circuit which as here shown includes a direct current track relay DR connected across the rails at the entrance end of the section and a track battery it connected across the rails at the exit end of the section. It follows that when the section DE is unoccupied, that is, when a train, shown conventionally at TN is not present in the section, the track relay DR is energized by the current supplied to the rails by battery I?! but that when the train TN occupies the section so that its wheels and axles shunt the rails, the relay DR is deenerized and released. The relay DR would be used to control signal and other circuits in any of the well-known arrangements but which signal circuits are not shown for the sake of simplicity since they form no part of my present invention.

In the drawing the track relay DR also governs a line circuit for an approach relay AR located at the exit end of the section, the arrangement being such that when the relay DR is energized closing its front contact H, the line circuit is closed and the approach relay AB is energized by cru'rent supplied to the line circuit from a source, the terminals of which are indicated at B and N. When a train enters the section DE shunting the track relay DR, the relay is released opening its front contact I I to interrupt the line circuit and the approach relay AR is deenergized and released closing its back contact I2.

The track circuit for the section DE is also provided with a source of alternating current and alternating current is at times superimposed on the direct current supplied to the track rails and which alternating current is available for control of cab signal apparatus. A track transformer I3 is provided with a primary winding i l and a secondary winding l5. The primary winding 14 is connected to a source of alternating current, the terminals of which are indicated at BX and NX. Specifically, the connection for the primary winding l4 extends from terminal BX of the alternating current source through back contact I2 of the approach relay AR, primary winding l4 and a trafiic controlled contact i6 of a track relay for the section next in advance, to terminal NX. The secondary Winding E5 of the track transformer 13 is interposed in series with the connection of battery It to the track rails. Consequently, when the approach relay AR'is released closing back contact l2 and the traffic conditions in advance of the section DE are such that the contact I6 is closed, the pri- 4 mary winding 14 is energized and alternating current is supplied from the secondary winding E5 of the track transformer to the track rails of the section DE. The alternating current Source BXNX may be of the commercial frequency of 60 cycles per second or it may be a special frequency of the order of or cycles per second, which is often used in cab signal systems. It is to be understood that the inven tion is not limited to these frequencies and other frequencies can be used.

The train TN is equipped with cab signal and train control apparatus which includes as essential elements a pair of inductors ll and I8, a receiver RC and a coding means or code modulator CM. The inductors I7 and I8 are mounted on the train ahead of the leading pair of wheels and in inductive relation with the rails. Thus, an electromotive force is induced in each of the inductors due to the alternating current supplied to the rails through the track transformer [3. The electromotive force thus induced in the inductors is of a value proportional to the magnitude of the alternating current flowing in the rails and it has the same frequency and characteristics as the rail current.

The two inductors Il and I8 are connected in series for adding their electromotive forces when the alternating current flowing in the track rails flows in the rails in opposite directions at any given instant. The inductors l1 and It are connected across the input terminals 19 and 2% of the receiver RC, the connection to the terminal is including a limiting resistor 2i and a tuning capacitor 22. Thus the inductors ii and I8 serve as a source of alternating signaling current for the receiver RC due to the electromotive force induced therein by the alternating current flowing in the track rails.

The receiver RC which is indicated as a whole by the dot and dash rectangle, may be any one of several different forms of receivers which are selectively responsive to coded alternating current and, as stated hereinbefore, this receiver may be similar to that shown in the Allison Patent No. 2,4614%. Such receivers will include an amplifier unit which in the drawing is indicated as a whole by the dotted rectangle AM. This amplifier unit includes an input transformer 23, an electron tube ET, an output or master transformer MT, a code following relay MR and a decoding transformer DT. The receiver RC is supplied with power from a convenient train car-- ried source, the terminals of which are indicated at B32 and N 32, the terminal B32 being the positive terminal. The train carried source would usually be the 32 volt direct current train lighting generator or battery but other sources of power may be used. A voltage divider comprising resistors RI and R2 in series is connected across the power source to provide the different voltages required for the amplifier unit AM.

The tube ET is shown as an indirectly heated tetrode which is designed for operation from a 32 volt source of direct current, but other types of tubes can be used. A heater 2c is connected across the power source through a resistor R3 and the tube ET is constantly heated. An anodecathode circuit for the tube is formed from the positive terminal B32 through a primary winding 25 of the master transformer MT, anode 25 and tube space to cathode 2'; and thence to the junction terminal of the two resistors R! and R2 of the voltage divider. The screen grid 28 of the when 15* connected to the'high voltagesideof the volt'a'ge divider and" preferably the primary winding" 25'' of the master transformer MT is" provided vvith"a"'by pass""capacitor 50:" The con: trol grid"2-"9 of the" tubis connected'to the nega'=' tive terminal-N32 tnriougnscondan winding 31) Oftli input ti'aris'forinei" ZEj-this 6611" titiofrfor ls. and .2 1:

' M r and'the" renyf' is operated in step with the impulses of: eleotroniotiv'e" force induced in; the se'onflary winding: 3:2: due to variations of the anode? current fiow'ing in winding 25; therelav'QMR'being' operated to one position in rlpbif1eft0 an ifi ese 19 h? anode. and operatedto its oth er position in response to a decrease in the anode current. i

It xvill ioe understood that the invention is not ite tome di w re h u e ET biased to cutofi and an adjustment of the tube can he usegi here the bias of the tube is such that a given value of anode" current" normally flows and the current is varied above'and below this; given value. 4 A

As here shown; the decoding transformerDT'is an autotransformer having a portion of-its wind ing; 35; upp1ied with" direct current from the- B32-N32 source when'the armature 33 of the master relay is operated to one of 'its1positions" and; another portion" of the "winding 3 5 is supplied withidirect current when the armature 33" is operated'to its other position. it followsthatan alternating electror'notive" force is developed acroSsWhewihding 35- when the relay MR is' operated; the frequency of the eleetr'ornotive farce? fi ifi 39 1. a. closed position of the switch wiiidihg 41' of the trair'1sfoifineit T l; connectlo lat of a a "aeitor 43 and thence athdee1 d" across the inpu "fai dfw f upperitenmnal-of th i W n g 1118* ni s e a them erm n 11: ee re' ct'ifie'r R4, one" blade of the switch 36 a wir'e' ifi,aiid'the'lovger term V ary winding" 54 being 2 connected? to the} input terrn ina'l lam g It is" to be p'oiiitec'l out tlfat the resistor dir'may not b ded-.

The asymmetric Jinit R4 is preferably a half wa ve:rectifier element; such as a ger anium? crystal, a copper oxide rectifier or' a S'lfrfil'lllf i f i fieii Th s the ut f dsbillatqr V I inpu fterminals ZU'oftlie receiver RCin series with the In; descr bing: thefio'peration of the apparatus I shall assurne' that; the switch 36" is'lplo sedsof that"the os'eillator*V! is activeand the-bur '13 thereof is" connected to the input terminals J's an'df20 r; the receive'r RC. It'is to be r efalleii that the" alte rriating voltage"supplied by the in duct 1 ljia nd- I Bfis of-the orde'r offlOOcYc per'seconfland that"the*frequency of the dsc latoris of the order of 3 cycles per second. Dur' ine p 'na f eycl'eofjtheoscillator" wage; t i v s; fag ihsihel xsy. ie; new we t (5 0f. the seor'idary" windi f 5' viewed in.

r ieerec't tubelff'isshowrias a tetifoa bfie tube spaceto catlioiiei 40 an aporti'ori of th drawing is the positive terminal, the rectifier unit R4 is nonconductive thereto. During this half cycle period of the oscillator, one half cycle of the 100 cycle signaling current is blocked out from the path through the oscillator output winding 54 by the rectifier R4 and during the other half cycle of the signaling current the oscillator voltage opposes the flow of the signaling energy through the winding 54. Thus the 100 cycle alternating current supplied to the input winding 3i of the receiver is little attenuated during the half cycle of the oscillator the rectifier R4 is blocking. During the half cycle of the oscillator voltage the top terminal of the winding 54 is the positive terminal the rectifier unit R4 is conductive thereof. The parts are proportioned so that the oscillator voltage is relatively high as compared with the signaling voltage as impressed upon the input terminals l9 and20 of the receiver. Furthermore, the rectifier R4 is selected to be worked at a relatively high portion of its nonlinear characteristic. Consequently, the path through the oscillator winding 54 and the rectifier R4 substantially shuntsboth half cycles of the signaling voltage during the half cycle that the oscillator voltage is passed by the rectifier R4 and substantially no signaling voltage is supplied to the input winding 3| of the receiver RC. In other words, the oscillator VI is a low impedance source connected in multiple with a high impedance source during this one half cycle of the oscillator voltage and the high impedance source comprising the inductors I! and I8 is in effect short-circuited. The energy supplied from the oscillator to the receiver winding 3| is of such a low frequency that it has little or no effect on the amplifier AM which is tuned to the relativel high frequency signaling current.

It follows from the foregoing that the signaling .voltage from the inductors I! and i8 is supplied to the amplifier AM at substantially full value during one half cycle of the oscillator voltage and the signaling voltage is substantially shunted and reduced to substantially zero value during the other half cycle of this oscillator voltage. Consequentl the signaling voltage as supplied to the amplifier of the receiver is coded by being periodically varied at the code rate of 180 times per minute or 3 times per second, that is, at a code rate corresponding to the frequency of the oscillator.

The net result of this action is that the receiver RC is energized at a code rate corresponding to the frequency of the oscillator, the code following relay NIH. is code operated at a rate corresponding to the frequency of the coding means in response to noncoded signaling current supplied by the inductors I1 and i8, and a clear signal indication or an indication corresponding to the frequency of the oscillator Vi is effected notwithstanding the fact that the signaling current supplied to the track circuit is noncoded.

It is to be observed that the tuning capacitor 43 of the oscillator is provided with four lead wires, two to each of its plates, and each plate is included in series in a circuit and an open circuit due to a defective plate of the capacitor will render the oscillator inoperative and the fault will be immediately detected by the receiver RC not being operated to provide a proper cab signal.

The coding means or code modulator here provided has the advantages that it has no moving parts. it is comparatively simple and of small construction so it can be mounted in the usual equipment box provided for housing an associated receiver. In practicing the invention I have found that the coding means here disclosed will provide satisfactory and reliable operation over a wide variation in temperature and also over a relatively wide variation in the voltage of the power source.

As stated hereinbefore, the electronic coding means here provided is not limited in its use to train carried apparatus. For example, it is apparent that the coding means could be used with the wayside apparatus to code the signaling current as it is supplied to the track circuit. Furthermore, while a half-wave rectifier is employed in the output of the oscillator, it is apparent that a so-called full-wave bridge type rectifier unit could be used in the output of the oscillator and the signaling current coded in a manner similar to that accomplished by the coding means here provided.

Although I have herein shown and described but one form of electronic coding means for signaling systems embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In a signaling system, the combination comprising, a winding to be energized by an alternating current of a given frequency and coded by being periodically varied at a given code rate, a source of alternating current of said given frequency, a circuit to connect said source to said winding and including inductance and capacitance to tune the circuit to resonance at said given frequency, an oscillator generating an alternating voltage of a frequency equal to said code rate, a nonlinear device, another circuit to connect said oscillator and device in series to said winding in multiple with said source, and said another circuit varying the alternating current of said source supplied to said winding at a code rate equal to the frequency of the oscillator voltage due to said nonlinear device.

2. In a signaling system, the combination comprising, a circuit element to be energized by an alternating current of a given frequency and coded by being periodically varied at a given code rate, a source of alternating current of said given frequency, means to connect said source to said circuit element, coding means including an electron tube oscillator and a rectifier, said oscillator operable to generate oscillations of a frequency equal to said given code rate and having an output winding to which said oscillations are supplied, said output winding and said rectifier in series connected to said circuit element in multiple with said source, and said coding means substantially suppressing said alternating current during alternate half cycles of said oscillations due to said rectifier and thereby coding at said given code rate the energization of said circuit element by said alternating current.

3. In a signaling system, the combination comprising, a winding to be energized by an alternating current of a given frequency and coded by being periodically varied at a given code rate, a source of alternating current of said given frequency, a circuit to connect said source to said winding and including inductance and capacitance to tune the circuit to resonance at said given frequency, coding means including an elec- FY91? El W QEQ CQ Qfi Qti en f 9.50. "late pr r le t g n rat as .at n p a ir ,quency equaltos d given ,coderate andof a voltagerelatively h1gli cornpared to the voltage @ffiflid a te n tin i t a i ssi at h vin an tse Windin to .sp sa ce llati ns ar sup i d and dmi pu 112s and endors t e se e refiner es t a ,fir r enii ne Wi in l mu tipl W391?- ??id .SQH QQ w e eby s Gliding m anubstant al asn esse sa a rn ting u r n d in al ercat hai ycl o t s il t pn ar t th volta and th n l n aract r ti o s 1, fliififi filldfih fi zm n o ed n insi e er zedpva t na ing current coded at said given code rate.

I mb n tions W ndinaas9sret al n g voltage 9 a rela 1 1y 1 11 .e u.. n i c me n towgnegt fls li c t .sa wii fling and including capacitance to tune the circuit "to" resonance at said h frequency, an oscillator generating an alternating voltage of ,a relatively low frequency, rectifying means, an- ;other circuit to connect said oscillator and rectisfy-ing-means to said winding in multiple with said source, said another circuit yin eiffectshpnting -saidalternating voltage, of high frequency away .I in iliir n itlt eh lf c le-9 th low frequency alternating vqltage said, rectifying means is conductive vvhereby the energy supplied i Winding is erl qdicell ,ra e 'a anod rate, corresponding to sai d low frequency, and signalling means controlled by the coded ener y thus suppliedto said winding.

omb n anlinpu circu ts q rcaof alternating signaling voltage of a given frequency, circuit meansto couple said sourceto said input eirwit for receiv ng energ thereto said circuit means includingcapacitance to tune the circuit rneans to resonance at said given frequency, an oscillator generating an alternating v l of a lisallcncyllowenthan said given frequency, a current rectifier, another circuit to connect said oscillator and said rectifier to said input circuit in multiple with said source, said another circuit in efiect shunting said signaling voltage during the half cycle of the oscillator voltage said rectifier is conductive due to the nonlinear characteristic of the rectifier whereby the energy supplied to said input circuit b said source is periodically varied at a code rate determined by the frequency of said oscillator, and signaling means controlled by said input circuit responsive to said coding of the signaling voltage.

6. In combination, signaling means efiectively responsive to alternating voltage which is coded by being periodic-ally varied at a given code rate, a source of noncoded alternating voltage having connections to said signaling means for supplying energy thereto, said alternating voltage being of a frequency higher than said code rate, an oscillator generating oscillations of a frequency equal to said given code rate, an asymmetric device, and means to connect said oscillator and said device to said signaling means in such a manner as to effectively shunt said source of alternating voltage on alternate half cycles of said oscillations.

'7. In combination, a receiver including an amplifier and a relay operable in response to an alternating voltage of a given frequency and coded at a given code rate, said receiver having an input circuit tuned to resonance at said given frequency, a source of alternating current of said given frequency having connections for supplying its energy to said input circuit, coding means s e t fi r a he eb or n t ee Q sHn a al a atir vol a ded b be erio i al ins no 9l qwins re -,1 su p ied w th recu ren including an electron tube, oscillator. generating an alternating voltage of a ireguency equal to input circuit, and said I another circuit in efiect suppressing the alternating voltage of said source supplied to said input circuit during alternate half cyclesof said oscillatorvoltage due to p i to a in u r u a sa g ven cod rat 8- wmb a m a sisn nslreqe v in lusnsa. cqq t ss-ensu relay, eansqperab wh v i d a a sir n d se ar i s s i d theret said rece v having asa i n .ir nal$i whi sa re m an ls nnectedhl ntr i cu e vin a time no c d 4 mat t su rea sm lectr callvs unlcdtdi a i lit-t rniuals fer supplying .an alternating voltage he os nsmeans n wi ns a Oscillato an a rectifier, sa d.csc atc c able tos nerat .cs ill on Of a .fr quenq aua can s re code rate, said oscillator connect dto said input erm na s in s r es w t sa d IQQPEfi ..tO,imP Q alternate half cycles of said oscillationscn said terminals, and said oscillator .connections and th os i lat ons en ated b ne,o.- lla o su tant e l u pre s ns sais fla iemat ns lvoltas' supplied by said control circuit at said coderate r ill i' fifi d r l 13%! i 1 to sa d nmd fi t raatin cu ren of the ist-" circuit.

.cqmbmat on a isns ir-sr eive i cl s- ,mean pe ted ..yvhen lses of alternating v a 9 i e n d at rs 1 t e s i e ei e swe test phi re a m an .is lln ci l ,c sirp c lia- 7 i 1 s- 9sivi sn ns deda t rsainasurtgn a re ativ l higl'fimpedance inductor coupled to said control circuit and connected across said terminals to impress on the terminals a noncoded alternating voltage in response to said control circuit current, an electron tube oscillator tuned to generate oscillations of a frequency substantiall equal to said code rate, a half-wave rectifier, a relatively low impedance winding receiving said oscillations from said oscillator, circuit means including said winding and said rectifier in series connected across said terminals, and said circuit means forming a low impedance path in multiple with said high impedance inductor which substantially suppresses said noncoded alternating voltage dur ing the half cycles of the oscillations passed by said rectifier and said relay means is supplied with pulses of alternating voltage of said code rate in response to said noncoded alternating current of the control circuit.

10. In combination, a receiving means which is operable in response to periodic interruptions of alternating voltage at different selected code rates, a pair of terminals across which said receiving means is connected, a control circuit which is supplied with noncoded alternating current, an inductor coupled to said control circuit and connected across said terminals for supplying thereto noncoded alternating voltage in response to said control circuit current, an oscillator operable to supply to an output winding an alternating voltage of a frequency substantially equal to a selected one of said code rates, a half- WEW r ct fie ci cuit means including said out- 11 put winding and said rectifier in series connected across said terminals, and said output winding and rectifier proportioned in such a manner as to substantially shunt said alternating voltage during the half cycle of said oscillator voltage the rectifier is conducting to substantially interrupt said noncoded alternating voltage at the frequency of said oscillations for operation of the receiving means in response to the noncoded current of the control circuit.

11. In combination, a receiving means which is operable in response to periodic variations of alternating voltage at diiferent selected code rates, a pair of terminals across which said receiving means is connected, a control circuit which is supplied with noncoded alternating current, an inductor coupled to said control circuit and connected across said terminals for supplying thereto noncoded alternating voltage in response to said control circuit current, an electron tube oscillator tuned to generate oscillations of a frequency corresponding to a selected one of said code rates, an output Winding receiving said oscillations from said oscillator, a half-wave rectifier, circuit means including said output winding and said rectifier connected across said pair of terminals, said output winding and rectifier proportioned to form a low impedance path during the half cycle said rectifier is conducting and substantially suppress at said terminals said voltage supplied by said inductor whereby the inductor voltage applied to the receiving means is periodically varied at said selected code rate.

12. In a signaling system, a code following relay means responsive to alternating voltage which is periodically interrupted at a given code rate, a transformer having a primary and a secondary winding, said secondary winding being con nected to said relay means, an inductor receiving at times a noncoded alternating voltage and connected to said primary winding to suppl said alternating voltage thereto; a code modulator including an electron tube oscillator, an output winding and a half-wave rectifier; said oscillator tuned to generate oscillations of a frequency equal to said given code rate, said output winding coupled to said oscillator to receive said oscillations, said output winding and rectifier in series connected to said primary winding in multiple with said inductor, said output winding having a relatively low impedance compared to the impedance of said inductor and the output winding substantially shunts said inductor during the half cycles of said oscillations the rectifier is conducting whereby the voltage of said inductor is substantially interrupted at said code rate and said relay means is operated in response to said noncoded alternating voltage received by the inductor.

13. In combination, a signaling receiver including a code responsive relay means operable when an alternating voltage coded by being periodically varied at a given code rate is supplied thereto, said receiver having a pair of input terminals to which said relay means is connected, a control circuit receiving at times noncoded alternating current and electrically coupled to said input terminals for supplying said alternating voltage thereto, a code modulator including an electron tube oscillator and a half-wave rectifier, said oscillator tuned to generate oscillations of a frequency corresponding to said given code rate, a winding adapted to receive said oscillations from the oscillator, circuit means including said winding and said rectifier in series connected to said input terminals to impress alternate half cycles of the oscillations on the terminals, and said circuit means and the oscillations effective to code said alternating voltage at said code rate for said relay means to be operated in response to said noncoded alternating current of the control circuit.

CARL VOLZ.

No references cited. 

